Each Spootnik account provides a WebDAV interface which lets OmniFocus clients communicate with Spootnik (see also "What's about OmniFocus for iPad/iPhone/iPod Touch?").

After being connected to Basecamp, Spootnik creates a new folder inside OmniFocus for each Basecamp project you'd like to share. This will be the only thing that gets synchronized between OmniFocus and Basecamp. Thus, if Spootnik should create a to-do list inside Basecamp you have to create or move a (OmniFocus) Project into this newly created folder. Spootnik only modifies items that were created (either in OmniFocus or Basecamp) by Spootnik. It doesn't do any kind of a magic merging between Basecamp and OmniFocus.

In short:
1. Basecamp project = OmniFocus folder
2. Basecamp to-do list = OmniFocus project
3. Basecamp to-do = OmniFocus task
... and everything outside folders created by Spootnik won't get synchronized to Basecamp.

Conclusion: Every user can share to-do's with Basecamp and maintain its own OmniFocus database where for example also private stuff can reside in. Read more here: Different Faces of Spootnik.
Spootnik starts a synchronization every 15 minutes. All changes made in OmniFocus will be applied to the respective Basecamp project and vice versa.

BUT. It happens sometimes that Basecamp changes doesn't appear every 15 minutes inside OmniFocus.

Why? Spootnik tries to treat 37signals resources as good as possible in the sense of making as few as possible requests to Basecamp. As for now it uses the Basecamp Project RSS Feed to detect if Basecamp did change. Unfortunately the RSS Feed doesn't cover all possible kind of changes. To lessen this weakness a bit, Spootnik ignores the Basecamp Project RSS Feed at least once a day.

In short: It's all about preserving resources. You always have the possibility to manually force a sychronization by pressing the "fast-forward" button in the upper right corner of your Spootnik account.
Spootnik provides a WebDAV interface which lets you connect OmniFocus and OmniFocus for iPad/iPhone/iPod Touch like you would connect it using another WebDAV service (e.g. MobileMe). If you use Spootnik you can't use the "Bonjour" option. This is a limitation of OmniFocus that has also a positive side. Everything you do on your iPad or iPhone will be directly synchronized to Basecamp without having to power-up your Mac.
Yes. You can move the folder created by Spootnik (which resides initially on the main level) below another one without affecting the synchronization. Thus, you can group shared folders (e.g. below a common "Work" folder).
Yes. But Spootnik won't rename the respective project name inside Basecamp. And if you rename a Basecamp project Spootnik won't rename the respective OmniFocus folder either.
If you move an OmniFocus project (or task) out of the OmniFocus folder created by Spootnik, the corresponding Basecamp to-do list or to-do item will not be deleted. But Spootnik remembers those items and will reconnect if moving them back again.
Select the project inside OmniFocus where you would like to set a default Context. Press "Inspect" or choose "Inspectors / Show Inspectors" inside the Menu and choose the Default Project.

Spootnik will consider this Context when creating new tasks out of Basecamp to-dos.
Yes. Spootnik doesn't synchronize the "Dropped" status and keeps on synchronizing its contents. Thus, it's a possibility to remove a project from a OmniFocus perspective without deleting it inside Basecamp.
If you uncheck the option "Only todos where I'm or anyone is responsible", all tasks inside the respective Basecamp project will be synchronized to OmniFocus.

If you leave this option checked, Spootnik will only synchronize tasks where you or anyone is responsible for.
If you synchronize all tasks of a Basecamp project to OmniFocus (see above), Spootnik creates a Context for each responsible party already assigned to a Basecamp todo.

You can then move this Context around or rename it inside OmniFocus without affecting the data inside Basecamp. If you delete a Context, the responsibility of the assigned tasks will change to yourself. By assigning a task to such a Context inside OmniFocus, Spootnik will attach the respective responsible party inside Basecamp.
The Basecamp generated password for OpenID doesn't work anymore. Spootnik will receive an "Authorization Required (401)" response from Basecamp. You can go around that limitation by grabbing a new 37signals ID.

How to grab a new 37signals ID
Switch to Basecamp and press "My Info" (on top right) first and "Edit your personal identification" afterwards. You should then be able to select "Or use a normal username" (the grey link) and enter a new username. That will be the username/password Spootnik needs to connect to your Basecamp account.

Now go to your Spootnik settings, press the edit link and enter your new username/password.
Before third party tools like Spootnik can access your data inside Basecamp, you have to enable the "Basecamp API".

Your account owner can enable the API by going to the Settings tab, then clicking the API link at the top of the page. More...
Security & Integrity
Spootnik doesn't store any Basecamp passwords since the introduction of 37signalsID. It just stores a token which Spootnik gets from Basecamp when you enter your credentials on Spootnik's settings page.

Your OmniFocus data sits on the same server as the synchronization runs. All communication between OmniFocus and this server is secured by SSL. If you enable "SSL 128-bit encryption" for your Basecamp account (on the bottom of the Settings tab) even the communication between Spootnik and Basecamp will be encrypted.

Have also a look at Spootnik's Privacy Policy and don't hesitate to write me if you have any further questions.
I'm constantly keeping an eye on Spootnik, analyze each failure and do my best to get an explanation for every case. I monitor only on an abstract level and will never look directly into your data without an explicit permission from you.

Comments are directly inside Spootnik's history (see right). If the failure was serious or did stop your synchronization, I will also notify you by email.
Nobody is perfect. The only thing you can do is to be prepared for the exceptional case. Thus to backup your data is very important.

OmniFocus has a built-in backup system. It automatically backs up your database once a day to ~/Documents/OmniFocus Backups/. You can easily change these settings inside the General pane of OmniFocus' Preferences.

To manually back up your database, choose Back Up Database from the File menu. To restore a backed-up version of your database, choose Revert to Database Backup from the File menu, then choose a backup file to use.
Unfortunately there is no possibility to make a backup of your Basecamp data except to export them. You can find the link inside the Account (Upgrade/Billing) tab.

But Spootnik has some built in trust-enhancement-features:
  1. It reports each change transparently inside the History tab.
  2. You can not delete a project over Spootnik. If you delete the Folder inside OmniFocus it will only disconnect the synchronization between OmniFocus and Basecamp. But it won't delete your Basecamp Project.
Account & Billing
"Interval 15 Minutes" refers to the interval Spootnik is synchronizing automatically with Basecamp. But you can force a Basecamp synchronization at any time by pressing the fast-forward button. This interval doesn't restrict your OmniFocus synchronization (e.g. Mac to iPhone).
It's the simplest and most reliant solution I'm able to implement at the moment. You can buy credit inside the "Billing" section and Spootnik charges its monthly fee on your credit balance. Any remaining credit balance will of course be refunded on cancellation. All you have to do is to make sure your credit balance isn't getting too low.

New: You're now able to set up an auto-recharge. It's implemented via PayPal subscription mechanism and thus requires a PayPal account. You can set it up inside the "Billing" section.
Missing Features
Spootnik doesn't synchronize the sort order between OmniFocus and Basecamp. In other words, if you change the order in Basecamp or OmniFocus it won't have an effect on the other side. But if you add new items inside Basecamp or OmniFocus, they will be added in the same order on the other side.
Unfortunately there's no nice way to convert an OmniFocus note into a Basecamp comment. But Spootnik has a "light" integration. If a Basecamp to-do item contains comments, Spootnik will put a link into the note of its respective OmniFocus task. That link will open your default browser and show the comments.

If you're interested, here are some problems converting an OmniFocus note into a Basecamp comment:
  • How to separate OmniFocus notes (e.g. dash, line-break, ...)
  • Basecamp comments are frozen after 15 minutes, OmniFocus notes are changeable without limitations
  • Can't change other users' comments
  • How to handle images/attachments. There are some limitation with Basecamp (e.g. downloading)
I know, there are a lot of To-do tools out there which would be nice to integrate. To be honest supporting Highrise and Backpack was one of my original thoughts. Because each of these systems have their own tasks which could be brought together inside OmniFocus.

But I won't do anything out of the blue. I will listen closely to the crowd using Spootnik. So tell me if and which tool you would like to have integrated.